The engine computer monitors the pressure from the fuel filter to know when it needs to be changed. It is a function of the amount of fuel burned and type of fuel. Towing and getting 10 MPG the filter will need to be changed more often than if driving the truck with no load. The same applies to DEF where my LML burns about a gallon every 750 miles with a load and goes about 1000 miles with no load.
The only concern I have with the fuel filter would be if I was using B20 biodiesel fuel as it can cause a host of problems and these are not covered under the GM warranty. You especially don't want to switch back and forth between B20 and regular diesel fuel.
I consider heavy loads or towing to be severe duty and for that GM has a different oil change schedule. I have the truck driven in these conditions half the time so I adjusted the oil change schedule to being every 7500 miles instead of roughly 10,000 miles per the DIC.
The Allison external filter should be changed at 7500 miles and then per the schedule which depends on the type of ATF used, type TES 389 versus TES 295. ATF needs to be changed every 24 months with the dealer supplied TES 389 or every 48 months with TES 295 which is available at Allison shops.
The front end needs to be greased every 3,000 miles and I bought a pistol type grease gun and right angle fitting to make this as easy as possible to do myself without a hoist.
I found that the stock GM air filter is better than the more expensive after market ones from Fram and others companies.
You can of course change the oil and filters more often if you have money to burn.
This is my maintenance schedule for my LML Duramax gleaned from the 3 manuals provided:
7,500 miles - change external transmission filter, rotate tires, torque wheel nuts -140 ft lb
15,000 miles - rotate tires, torque wheel nuts, check air filter
22,500 miles - rotate tires, torque wheel nuts
25,000 miles - change engine oil, lube front suspension, steering linkage, cables, change trans fluid and filter (assumes use of TES 389 fluid - should change to TES 295 and triple mileage interval to every 75K miles at most)
30,000 miles - rotate tires, torque wheel nuts, check air filter
35,000 miles - rotate tires, torque wheel nuts
45,000 miles - rotate tires, torque wheel nuts, check air filter
52,500 - rotate tires, torque wheel nuts, change engine oil and filter, lube front suspension, steering linkage, cables replace air filter, change trans fluid and filter
60,000 miles - rotate tires, torque wheel nuts, change engine oil and filter, check air filter
67,500 miles - rotate tires, torque wheel nuts, change engine oil and filter,
75,000 miles - rotate tires, torque wheel nuts, change engine oil and filter, check air filter,
lube front suspension, steering linkage, cables, change trans fluid and filter
82,500 miles - rotate tires, torque wheel nuts, check air filter
90,000 miles - change engine oil and filter, check air filter
97,500 - rotate tires, check air filter, change engine oil and filter, change transfer case fluid, trans fluid and filter, change air filter, lube front suspension, steering linkage, and cables
105,000 miles - rotate tires, torque wheel nuts, change engine oil and filter, check air filter
112,500 miles - rotate tires, torque wheel nuts, change engine oil and filter, check air filter
120,000 miles - rotate tires, torque wheel nuts, change engine oil and filter, check air filter
127,500 miles - rotate tires, lube front suspension, steering linkage, cables, check air filter
150K or every 5 years flush system and change coolant (whichever comes first}
Change trans fluid and filter every 25K miles or 24 months - TES 389 type
Fuel filter - change when indicated by the engine or every 2 years.
(life depends upon the fuel cleanliness and use of biodiesel )
